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Singing glasses helps you demonstrate how a glass resonates when the driving force meets the natural force of the glass which causes it to vibrate and produce sound its something fun to play around with and you learn along with it.
Materials:
Two wine glasses
Water
Toothpicks
How to make it work :
Fill each glass with equal amounts of water (half-full)
Hold the leg of the glass with one hand and dip your middle finger of your other hand into the water.
Put your finger slightly on the rim of the glass, press down and rub it all the way around the rim without stopping. Keep going all around the rim of the glass while still giving pressure. That should make the glass sing.
Once you've made the glass sing, do the same thing with the other wine glass. You want the tone from each glass to be the same. This means that you will need to adjust the amount of water in each glass so that the tone is exactly the same.
Rest the toothpick on the rim of one of the glasses. Put the second wine glass close to the first one, but make sure they're not touching. Dip your finger in the water and make the glass without the toothpick sing, observe the toothpick carefully. The toothpick moves? how?
Why do the glasses sing? Why does the toothpick move?
The singing of the wine glass occurs because as you rub your finger on the rim, your finger first sticks to the glass and then slides. The stick and slide action occurs in very short lengths and produces a vibration inside the glass which in return produces a sound. As soon as the first few vibrations are produced, the glass sings . That means the crystals in the glass are vibrating together and creating one clear tone. You can change the pitch by adding or subtracting the amount of water in the glass. The volume can be changed only a little bit by increasing or decreasing the pressure from your finger.
The movement of the toothpick is caused by vibration. Because there are equal amounts of water, the second glass vibrates at exactly the same frequency as the first. The sound waves produced by the first glass travel in every direction. When those sound waves reach the second glass, the glass begins to vibrate and the toothpick moves.
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